Arboriculture & Urban Forestry 32(6): November 2006 299 The importance of these classifications is that they serve as part of the decision making process used by the United States Department of Agriculture to determine which trees will be removed or treated with insecticides as part of eradication programs. Specifically, for Asian longhorned beetle, Sawyer (2003, 2005) indicated that trees in the very good, good, and occasional host categories were ones that are targeted for intervention. This means removal or treatment with insecti- cides in eradication areas. Trees on the questionable and no record list are not treated with insecticides in eradication programs for Asian longhorned beetle (Sawyer 2003, 2005). Current regulations in the central United States call for the containment, removal, and destruction of all ash trees within 200 to 800 m (220 to 880 yd) of a tree known to be infested in an outlying site (Siegart and McCullough 2006). The immediate impact on the local tree community is dra- matic when these exotic borers are detected and an eradica- tion program has been established. In New York and Chi- cago, more than 8,000 trees have been removed in an effort to slow the spread of Asian longhorned beetle. In 2005, in New York, more than 78,000 trees received insecticide treatments as part of the eradication effort on the basis of their suscep- tibility to Asian longhorned beetle (USDA 2005). The most recent eradication program for Asian longhorned beetle in Middlesex and Union counties in New Jersey called for the removal of more than 8,000 susceptible trees. Furthermore, program officials planned to treat approximately 20,000 ad- ditional susceptible trees with systemic insecticides at a cost of more than $12 million (USDA 2005). In Michigan alone, emerald ash borer has caused $11.6 million of damage to landscapes and nurseries and quarantines have restricted the sale of more than $2 million of nursery stock (Herms et al. 2004a). Cappaert et al. (2005) report that more than 15 mil- lion ash trees are dead or dying as the result of emerald ash borer in Michigan. Attempts have been made to project potential losses asso- ciated with these two invasive borers over larger geographic regions. Nowak et al. (2001) used tree inventories to estimate potential monetary losses resulting from Asian longhorned beetles in nine cities in the United States. The results of this analysis were staggering with an estimated potential loss of approximately 1.2 billion trees at a compensatory value of $669 billion. Potential costs associated with removals of ur- ban ash trees in the United States are estimated at $20 to 60 billion, a figure that does not include replacement costs (Cap- paert et al. 2005). The objective of our study was to assess the threat to street trees imposed by Asian longhorned beetle and emerald ash borer in 12 cities in eastern North America if they become established and eradication programs are put into place. We collected a sample of tree inventories, identified the most common genera of trees, and enumerated the proportion of trees that might be at risk if these borers escaped quarantines and became widespread. MATERIALS AND METHODS We obtained inventories of street trees from 12 cities and one college campus in the temperate zone of eastern North America. Asian longhorned beetle and emerald ash borer are expected to survive well in the cities in question. Cities in- cluded in the study were Wilmington, Delaware; Chicago, Illinois; Lincolnshire, Illinois; Marion, Indiana; Florence, Kentucky; Mt. Rainier, Maryland; Ann Arbor, Michigan; Kansas City, Missouri; New York City, New York; Gastonia, North Carolina; Toledo, Ohio; and Toronto, Ontario. The site in Toronto was the campus of the University of Toronto. All other sites were inventories of street trees. Inventories of trees were all conducted by ground survey using a variety of per- sonnel. In Florence, Gastonia, Kansas City, Lincolnshire, Marion, and Wilmington, inventories were conducted by pri- vate firms that specialized in developing inventories of street trees. In other cities such as Ann Arbor, Chicago, Mt. Rainier, New York City, and Toledo, inventories were conducted by trained urban foresters used by the city or state or by munici- pal employees and volunteers under their supervision. At the University of Toronto, the survey was conducted by the Fac- ulty of Forestry at the St. George Campus (Podolsky 2004). The number of trees included in the inventories and dates of the inventories used in this study were as follows: Wilming- ton (12,586: 2002), Chicago (416,000: 1991 to 1992), Lin- colnshire (3,688: 2003), Marion (6,357: 2003), Florence (6,323: 2002), Mt. Rainier (856: 1996), Ann Arbor (47,045: 1992 initial, continuous 2005), Kansas City (120,816: 2000 to 2001), New York City (453,372: 1995), Gastonia (1,510: 2002), Toledo (76,792: 1985 initial continuous 2005), and Toronto (2839: 2003). Inventories were conducted as com- plete surveys of all streets in most cities with the exception of Chicago where inventories were based on random samples that were used to extrapolate findings to a city-wide basis (Nowak 1994). To assess the risk of urban trees in the cities sampled in this study, we adopted the convention of Nowak et al. (2001), Sawyer (2003, 2005), and Siegert and McCullough (2006), namely that intervention decisions would be made at the ge- neric level and directed at genera known to be susceptible to attack by Asian longhorned beetle and emerald ash borer. For Asian longhorned beetle, this included trees in the very good, good, and occasional use categories enumerated by Sawyer (2003). Specific genera included Acer, Salix, and Ulmus in the very good category; Aesculus, Betula, and Platanus in the good category; and Albizzia, Celtis, Fraxinus, Populus, and Sorbus in the occasional use category. For emerald ash borer, trees in the genus Fraxinus were included (Seigert and Mc- Cullough 2006). ©2006 International Society of Arboriculture
November 2006
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